An Organic Light-Emitting Diode (OLED) display apparatus comprises a substrate, an anode, an organic film layer, a cathode, a packaging layer and a packaging coverplate, and has a bright application prospect for having advantages as follows: light weight, thinness, wide view angle, active light emission, continuous and adjustable colour of the emitted light, low cost, fast response, low energy consumption, low driving voltage, wide range of working temperatures, simple production process, high luminous efficiency and ability to realize flexible display. Thus, the OLED display apparatus attracts great attention in industrial and scientific fields.
Since interfaces between respective layers of the OLED have different refractive indexes, when light passes through these interfaces, with the occurrence of total internal reflection, photons finally exiting the surface of glass account for only 20% of a total amount of the photons, which will bring about problems as follows: (1) low output of light leads to a need to use a light-emitting material of high grade and to increase input current so as to meet the request of brightness, and thus results in increase in the cost and decrease in the service life; (2) energy that cannot be taken out (about 80%) will be converted into heat to increase the temperature of the organic functional layer, which will not only deteriorate the stability and photoelectric performance of the OLED, but also shorten the service life of the OLED; and (3) a heat dissipation device must be provided in order to eliminate influence of heat on the service life and performance of the OLED, which will increase the production cost. Therefore, it is necessary to design and improve the OLED device so as to improve the output of light.
Moreover, studies have shown that water vapor and oxygen in air have great influence on the service life of the OLED, and the reasons for this are mainly analyzed form the following aspects: when the OLED works, electrons are to be injected into the cathode, which requires the work function of the cathode to be as low as possible, however, metals for making the cathode such as aluminum, magnesium, calcium, etc, are usually active, and apt to react with water vapor penetrating therein. In addition, the water vapor will also react with a hole transport layer and an electron transport layer (ETL), and such reactions will cause failure of the device. Therefore, it is necessary to effectively package the OLED to separate the functional layers of the OLED device from the water vapor, oxygen and the like in air, whereby the service life of the device can be prolonged.